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Strava: Watts generated


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The Strava power estimate is rubbish.  A friend of mine rode the Cycle Challenge 100 yesterday at 38kph average speed. Strava had his average power at 453 watts. He weighs about 70 kilos and is a decent B batch rider. At best his wattage should 240 NP, with the average I guess around 195-205 watts.

Fark accuracy...think of the bragging rights :ph34r:  :ph34r:

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Power=Force(vector)(dot product) Velocity (Vector)

Velocity is easy , it is the velocity in m/s

Force is not so easy , There are 2 main contributors:

Drag force = 0.5 * density * Velocity^2 * Frontal area * Drag coefficient

Which is more or less equal to Drag force = 0.24*Velocity^2 (mountainbiker) and 0.186*Velocity^2 (road bike on drops)

Rolling resistance= mass(rider+bike) * gravitational acceleration * Rolling resistance coefficient

Which is equals : mass*9.8*0.014 (mountainbike) and mass*9.8*0.003 (road bike)

 

So you sum the forces and multiply it by velocity (in m/s) and that will give you power.

 

To answer your question about why it differs , the user inputs for bike type and mass are probably set incorrectly.

 

O and in a slipstream the drag force is decreased by 30% (if I recall correctly)

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Power=Force(vector) * (dot product) Velocity (Vector)

Velocity is easy , it is the velocity in m/s

Force is not so easy , There are 2 main contributors:

Drag force = 0.5 * density * Velocity^2 * Frontal area * Drag coefficient

Which is more or less equal to Drag force = 0.24*Velocity^2 (mountainbiker) and 0.186*Velocity^2 (road bike on drops)

Rolling resistance= mass(rider+bike) * gravitational acceleration * Rolling resistance coefficient

Which is equals : mass*9.8*0.014 (mountainbike) and mass*9.8*0.003 (road bike)

 

So you sum the forces and multiply it by velocity (in m/s) and that will give you power.

 

To answer your question about why it differs , the user inputs for bike type and mass are probably set incorrectly.

 

O and in a slipstream the drag force is decreased by 30% (if I recall correctly)

You must be fun at parties...

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Power=Force(vector)(dot product) Velocity (Vector)

Velocity is easy , it is the velocity in m/s

Force is not so easy , There are 2 main contributors:

Drag force = 0.5 * density * Velocity^2 * Frontal area * Drag coefficient

Which is more or less equal to Drag force = 0.24*Velocity^2 (mountainbiker) and 0.186*Velocity^2 (road bike on drops)

Rolling resistance= mass(rider+bike) * gravitational acceleration * Rolling resistance coefficient

Which is equals : mass*9.8*0.014 (mountainbike) and mass*9.8*0.003 (road bike)

 

So you sum the forces and multiply it by velocity (in m/s) and that will give you power.

 

To answer your question about why it differs , the user inputs for bike type and mass are probably set incorrectly.

 

O and in a slipstream the drag force is decreased by 30% (if I recall correctly)

Maybe you could also tell us: What is the airspeed velocity of an unladen swallow?

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Power=Force(vector)(dot product) Velocity (Vector)

Velocity is easy , it is the velocity in m/s

Force is not so easy , There are 2 main contributors:

Drag force = 0.5 * density * Velocity^2 * Frontal area * Drag coefficient

Which is more or less equal to Drag force = 0.24*Velocity^2 (mountainbiker) and 0.186*Velocity^2 (road bike on drops)

Rolling resistance= mass(rider+bike) * gravitational acceleration * Rolling resistance coefficient

Which is equals : mass*9.8*0.014 (mountainbike) and mass*9.8*0.003 (road bike)

 

So you sum the forces and multiply it by velocity (in m/s) and that will give you power.

 

To answer your question about why it differs , the user inputs for bike type and mass are probably set incorrectly.

 

O and in a slipstream the drag force is decreased by 30% (if I recall correctly)

 

Not a dig at Omicrom (if I understood the above I'm sure it would be interesting), more the industry;

 

I like riding my bicycle.

 

Still amazed how professionals in the 80s even managed to get out the front door without all the tech that is considered essential these days...

 

But yes, also, if someone can provide the air speed formula for a pair of laden African Swallows carrying a coconut by the husk I believe that we would get to the heart of the matter?

Edited by andrew5336
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Not a dig at Omicrom (if I understood the above I'm sure it would be interesting), more the industry;

 

I like riding my bicycle.

 

Still amazed how professionals in the 80s even managed to get out the front door without all the tech that is considered essential these days...

 

But yes, also, if someone can provide the air speed formula for a pair of laden African Swallows carrying a coconut by the husk I believe that we would get to the heart of the matter?

yes and no.

 

Getting bogged down by the data can strip the enjoyment out of riding, but in the 80s the only solution they had was to ride more, train more, no pain no gain.

Science has been able to focus the training and more specific areas and is now able to measure improvements better.

So if you're trying to get stronger/faster and not to worried about the enjoyment factor then the tech makes sense.

 

i went through a period where all I had was my phone in my back pocket recording the mileage. It was rather liberating to ride like that.

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yes and no.

 

Getting bogged down by the data can strip the enjoyment out of riding, but in the 80s the only solution they had was to ride more, train more, no pain no gain.

Science has been able to focus the training and more specific areas and is now able to measure improvements better.

So if you're trying to get stronger/faster and not to worried about the enjoyment factor then the tech makes sense.

 

i went through a period where all I had was my phone in my back pocket recording the mileage. It was rather liberating to ride like that.

 

For sure. I ride with a wrist Garmin and obviously am aware of speed etc and would love a unit with Strava segments just for fun.

 

I think that there are obvious benefits to tech advancements in terms of knowing more about nutrition, how much and the rough types of training to do (instead of just 100s of kms every day like the old guys did) but ask anyone about the most beautiful race wins on TV.

 

It's those where a rider pulls out his earpiece, ignores his computer and goes til he sees stars and collapses across the line a la van der Poel at Amstel Gold or when it comes down to 2 at Roubaix and is man on man instead of an obsessive watching of wattage with a team manager plotting the optimal output to keep a chase group at bay...

 

For me anyway.

 

And no pain no gain is a good life policy to be honest. This Millenial session with "Hacking" everything including fitness is nauseating.

 

HTFU kids - we don't go out there to be comfortable we go out there to get outdoors and out of our comfort zone to experience something different from the everyday mundane.

Edited by andrew5336
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For sure. I ride with a wrist Garmin and obviously am aware of speed etc and would love a unit with Strava segments just for fun.

 

I think that there are obvious benefits to tech advancements in terms of knowing more about nutrition, how much and the rough types of training to do (instead of just 100s of kms every day like the old guys did) but ask anyone about the most beautiful race wins on TV.

 

It's those where a rider pulls out his earpiece, ignores his computer and goes til he sees stars and collapses across the line a la van der Poel at Amstel Gold or when it comes down to 2 at Roubaix and is man on man instead of an obsessive watching of wattage with a team manager plotting the optimal output to keep a chase group at bay...

 

For me anyway.

 

And no pain no gain is a good life policy to be honest. This Millenial session with "Hacking" everything including fitness is nauseating.

 

HTFU kids - we don't go out there to be comfortable we go out there to get outdoors and out of our comfort zone to experience something different from the everyday mundane.

mostly agreed.

the guy who uses the tech for guidance but is in tune with his body and knows where and how much he can push without the tech telling will be the more exciting rider to watch.

 

Take max HR for example. I spent close to 60% of my time in the last race in zone 5, the rest in zone 4, so I started googling for any ill effects of staying that high. I came across many threads were guys were saying the 220-age formula was not their max HR.  

So if you stick to what the tech says (on default setting) you'll think you're blowing up, but if you know your body and go by feel you can push that bit more.

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For sure. I ride with a wrist Garmin and obviously am aware of speed etc and would love a unit with Strava segments just for fun.

 

I think that there are obvious benefits to tech advancements in terms of knowing more about nutrition, how much and the rough types of training to do (instead of just 100s of kms every day like the old guys did) but ask anyone about the most beautiful race wins on TV.

 

It's those where a rider pulls out his earpiece, ignores his computer and goes til he sees stars and collapses across the line a la van der Poel at Amstel Gold or when it comes down to 2 at Roubaix and is man on man instead of an obsessive watching of wattage with a team manager plotting the optimal output to keep a chase group at bay...

 

For me anyway.

 

And no pain no gain is a good life policy to be honest. This Millenial session with "Hacking" everything including fitness is nauseating.

 

HTFU kids - we don't go out there to be comfortable we go out there to get outdoors and out of our comfort zone to experience something different from the everyday mundane.

 

Ah the 80s and 90s, when you didn't know or couldn't really find out how strong your opponents are, so you dope to the gills, just short of overdose and hope its enough and that the testing hasn't caught up yet. Now at least they know to stop the doping or control their micro doping up until they have 1% more power output as their opponent and still below the doping radar.

 

Yes, it was thrilling racing at that time, but how credible really, not really more than currently.

 

Each to his own I guess. It makes a race interesting to see if the calculator can out-compute the traditional racer. If the ones spontaneous nature can outwit the the one on a set plan.

 

I like that there are variables to racing and that it isn't always the strongest winning.

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Ah the 80s and 90s, when you didn't know or couldn't really find out how strong your opponents are, so you dope to the gills, just short of overdose and hope its enough and that the testing hasn't caught up yet. Now at least they know to stop the doping or control their micro doping up until they have 1% more power output as their opponent and still below the doping radar.

 

Yes, it was thrilling racing at that time, but how credible really, not really more than currently.

 

Each to his own I guess. It makes a race interesting to see if the calculator can out-compute the traditional racer. If the ones spontaneous nature can outwit the the one on a set plan.

 

I like that there are variables to racing and that it isn't always the strongest winning.

I was educating a colleague at work about cycle races the other day.

We have a TV in the coffee lounge and he was watching a bit, so he asks "why doesnt anyone try and pass the guy in front, they all kinda just sit behind him in a V shape"

I started by explaining drafting and then went into strategies.

You could see the light-bulbs going on in his head and the interest increasing.

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yes and no.

 

Getting bogged down by the data can strip the enjoyment out of riding, but in the 80s the only solution they had was to ride more, train more, no pain no gain.

Science has been able to focus the training and more specific areas and is now able to measure improvements better.

So if you're trying to get stronger/faster and not to worried about the enjoyment factor then the tech makes sense.

 

i went through a period where all I had was my phone in my back pocket recording the mileage. It was rather liberating to ride like that.

You forgot that your training dairy and programs in those days were hand written.... and then there were spread sheets....

 

Phone in the back pocket..... pfffft

Money for the tikkie box

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Good morning

Trying to understand the logic behind the Watt figures that form part of the stats on any ride. 2 riders ride together on a 60km route. Once done both have identical average speeds, distance, climbing meters etc.

Why does one have a power output say of 150 watts and the other 90 watts? 

Thanks folks for all the interesting replies. Lots of info to digest :) but conclusion is that one cant rely too much of the Strava power stats. 

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You forgot that your training dairy and programs in those days were hand written.... and then there were spread sheets....

 

Phone in the back pocket..... pfffft

Money for the tikkie box

lotus 123 spreadsheet to work out gear ratios

there was no training diary, everything was in your head.

The height of tech was a cateye

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lotus 123 spreadsheet to work out gear ratios

there was no training diary, everything was in your head.

The height of tech was a cateye

Snap.  In the early 80's. I was lucky enough to have guidance from Wiele Wentzel.  So he developed a training program for me.  One pager, typed nogal...

 

Rode on feel for 12 years.  It all started to change when I bought my 1st HR monitor in '95.

 

HR of over 200!!! EISH!! SERIAAS!!

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As time passes Strava will tweak or change their algorithm for computing estimated power.

 

Also, regarding different readings, the estimated power can vary significantly between the device you use.

 

There is commonly a 10-25 watt difference between a Garmin Edge 1000 and iPhone. (The most common difference currently is about 10 watts on a ride.)

 

Also, some Strava estimated power as recorded by some devices is way off on wattage estimates for descents.

 

More important than the true or accurate measurement of what one's real wattage is as measured by a properly calibrated PM is that the Strava data is consistent. (Same effort in same circumstances using same device should be consistently the same.)

If it makes use of heart-rate it will also skew readings as towards the end of a ride where your heart-rate could be high but the watts would be less than at the same heart-rate when fresh.

 

But again if it is consistent it is something you can work with.

Edited by TDFN
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